Drop the password-manager pattern from alknet-vault (drift item #7,
ADR-025, resolves review #002 C9). Site-specific password derivation
is not relevant to an RPC system's vault.
Removed:
- derive_password method from VaultServiceHandle (service.rs)
- derive_password_string method from VaultServiceHandle (service.rs)
- site_password_path function from derivation.rs
- site-password derivation path row from derivation.rs doc table
- All password-derivation tests from service.rs and derivation.rs
- Now-unused base64 URL_SAFE_NO_PAD import from service.rs
Rename the crate from alknet-secret to alknet-vault to better reflect its
purpose as a local key vault (seed management, key derivation, encryption)
rather than a network service.
Symbol renames:
- SecretService → VaultService
- SecretServiceHandle → VaultServiceHandle
- SecretServiceActor → VaultServiceActor
- SecretServiceError → VaultServiceError
- SecretProtocol → VaultProtocol
- SecretMessage → VaultMessage
- ServiceLocked → VaultLocked
- alknet_secret → alknet_vault (crate name)
Update ADR-008 with vault access pattern: the vault is a capability source,
not a service endpoint. The CLI injects derived/decrypted material into
operation contexts — handlers never hold vault references.
